1. Field of the Invention
This invention relates to a multichannel audio amplification apparatus for reproducing a multichannel sound including a surround sound, and in particular to a multichannel audio amplification apparatus including a speaker terminal group TA for connecting an A-type speaker group including a surround speaker for reproducing only the surround sound and a speaker terminal group TB for connecting a B-type speaker group including no surround speaker.
2. Description of the Related Art
There is provided a multichannel audio amplification apparatus for reproducing a surround sound field by reproducing what is called a multichannel audio signal having a plurality of independent audio signal channels alone or with a video signal. With regard to the multichannel audio signal, various systems and formats have been proposed including directions of arranging speakers for respective channels, reproduction frequency bands and surround systems. In many cases, the multichannel audio signal may include totally five channels of signals having a front center signal C, a surround left signal SL and a surround right signal SR as well as a front left signal L and a front right signal R, or may include totally seven channels of signals further having a surround back left signal SBL and a surround back right signal SBR. Also, the multichannel audio signal may include what is called 5.1 channels or 7.1 channels of signals additionally having a bass signal LFE.
The multichannel sound is expected to be reproduced by a speaker group including a plurality of speakers connected to the multichannel audio amplification apparatus and arranged correspondingly to the respective channels. Front audio signals (including the front left signal L, the front right signal R and the front center signal C, as in all the cases described below) are reproduced by front speakers (including a front left speaker Lsp, a front right speaker Rsp and a front center speaker Csp, as in all the cases described below) arranged in front of a listener. Further, surround audio signals (including the surround left signal SL, the surround right signal SR, the surround back left signal SBL and the surround back right signal SBR, as in all the cases described below) are desirably reproduced by the surround speakers (including a surround left speaker SLsp, a surround right speaker SRsp, a surround back left speaker SBLsp and a surround back right speaker SBRsp, as in all the cases described below) respectively arranged on a side or behind the listener.
Assume the speaker group for reproducing the multichannel sound has a minimum configuration including only the front speakers arranged in front of the listener and no surround speaker for reproducing only the surround audio signal, specifically including only the front left speaker Lsp and the front right speaker Rsp for ordinary stereo reproduction. In such a case, the multichannel audio amplification apparatus generates a stereo audio signal obtained by mixing the surround audio signal into the front audio signal, which stereo audio signal is reproduced by the front speakers. Such a process of generating the stereo audio signal includes a down-mixing process (including a simple phase shift process and the like) of adding the surround audio signal to the front audio signal, and what is called a virtual surround process of adding an audio signal obtained by subjecting the surround audio signal to a virtual localization process based on the HRTF (Head Related Transfer Function) to the front audio signal. Incidentally, unless the stereo audio signal is generated by mixing the surround audio signal with the front audio signal, a problem would be posed that the surround audio signal cannot be reproduced by the front left speaker Lsp and the front right speaker Rsp.
Conventionally, two speaker groups including A and B types are connected to a single multichannel audio amplification apparatus, and one of the speaker groups of A and B types is used by switching therebetween (what is called “Speaker A or B”), or the speaker groups of A and B types are used simultaneously (what is called “Speaker A+B”). The A-type speaker group and the B-type speaker group are used by being arranged in an identical or different zones (an area such as one room, or an area for reproduction). In the most common method of use, the listener arranges the A-type speaker group in a first zone and the B-type speaker group in a second zone, so that, in a case where the multichannel sound is reproduced in the first zone, the multichannel audio amplification apparatus can be operated to output to the A-type speaker group while, in a case where the multichannel sound is reproduced in the second zone, the multichannel audio amplification apparatus can be operated to output to the B-type speaker group.
However, all the multichannel audio amplification apparatuses are not necessarily so configured that the surround speaker for reproducing only the surround sound can be connected to each of the two speaker groups of A and B types. Speaker terminals for connecting the front speakers and the surround speakers can be prepared for the speaker terminal group TA for connecting the A-type speaker group. For the speaker terminal group TB for connecting the B-type speaker group, on the other hand, only speaker terminals for connecting the front left speaker Lsp and the front right speaker Rsp for ordinary stereo reproduction may be prepared due to a limited space of a panel for installing the speaker terminals.
A conventional speaker connection circuit apparatus (Japanese Patent Publication for opposition No. 2003-32800) is available, including a speaker drive means for self-determining connection or non-connection of a speaker, a means for automatically changing a down-mix method based on the number of speakers connected and a multichannel audio system to be reproduced, and an amplification means for carrying out a predetermined down-mixing based on the number of speakers connected and the multichannel audio system to be reproduced and driving the speakers. Also, there is also conventionally available a sound reproduction apparatus (Japanese Patent Publication for opposition No. 2004-56418) including a mode setting means adapted to select one of a first mode with the A-type speaker group and the B-type speaker group arranged in the first zone and a second mode with the A-type speaker group arranged in the first zone and the B-type speaker group in the second zone. Also, there is available an apparatus having a set-up device (Japanese Patent Publication for opposition No. 11-243599) for, in order to detect the speakers connected to the multichannel audio amplification apparatus and specify setting conditions for each channel, inputting a test signal to the connected speaker and measuring a test sound reproduced by the test signal with a microphone to set a level and delay time.
In these conventional multichannel audio amplification apparatuses, assume that the listener operates to use the B-type speaker group including no surround speaker (for example, operation to turn on “speaker B”). Unless the process (hereinafter referred to a the mixing process) is executed to generate the stereo audio signal by mixing the surround audio signal with the front audio signal as described above, no surround audio signal component is reproduced by the B-type speaker group. Therefore, the mixing process is executed without regard to the configuration of the A-type speaker group connected. In a case where the listener operates the speaker configuration of the multichannel audio amplification apparatus to turn on the “speakers A+B”, therefore, the stereo audio signal subjected to the mixing process is reproduced by the front speakers in the zone with the A-type speaker group arranged therein and the surround speaker in the A-type speaker group cannot be used even when the A-type speaker group has the surround speaker.
Also, in some multichannel audio amplification apparatuses, a part of the terminals of the speaker terminal group TA occasionally double as those of the speaker terminal group TB for cost reduction. In this multichannel audio amplification apparatus, an operation for “speaker B setting” in a set-up menu is required. Specifically, the set-up menu includes “speaker B setting” for permitting the listener to preliminarily set by distinguishing whether the shared speaker terminal is connected with “the surround speaker of the A-type speaker group” or “the front speaker of the B-type speaker group”. In a case where the “speaker B setting” is on, for example, “the speaker B” but not “the surround speaker of the A-type speaker group” is connected to “the surround speaker terminal”, and the mixing process may be automatically set in spite of use of the A-type and/or B-type speaker groups.
Nevertheless, the listener not accustomed to the multichannel audio amplification apparatus may erroneously operate to “use the B-type speaker group”, resulting in that the listener may erroneously recognize a malfunction that “no surround sound is reproduced by the surround speaker of the A-type speaker group”. In such a case, even if the A-type speaker group has the surround speaker, the stereo audio signal subjected to the mixing process is reproduced by the front speakers and therefore no surround sound is reproduced by the surround speaker of the A-type speaker group in the zone with the A-type speaker group arranged therein. In the operation of the multichannel audio amplification apparatus, this may lead to misrecognition by the listener as a malfunction that “only the mixing process can be selected”. In a case where “the speaker B setting” is erroneously turned on, on the other hand, the listener may take it as a malfunction that “the front sound is reproduced by the surround speaker (of the A-type speaker group connected to the speaker terminal group TB which is shared as a matter of fact)”.
Specifically, assume that the listener erroneously operates or sets the multichannel audio amplification apparatus due to a fact that one of the two speaker groups of A and B types connected to the multichannel audio amplification apparatus cannot be connected with the surround speaker for reproducing only the surround sound. Then, the multichannel audio signal is required to be subjected to the mixing process substantially forcibly, thereby posing a problem that the misrecognition that the multichannel audio amplification apparatus malfunctions may occur to the listener. Also, provision of the mode setting means or the like gives rise to a problem that the setting operation of the multichannel audio amplification apparatus is complicated.